Wenyi Li1 Elijah Shirman2 Yu Wang1 Benedetto Marelli3 Beom Joon Kim1 Fiorenzo Omenetto1

1, Tufts University, Medford, Massachusetts, United States
2, Harvard University, Cambridge, Massachusetts, United States
3, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Printed electronics has attracted considerable interest as an alternative manufacturing process to realize circuits or devices on paper or plastic considering its low material consumption and fast accessibility. Using metallic nanoparticles to create conductive traces for lower cost and faster process has been extensively investigated, but often limited by the sintering process. Plasma sintering is widely employed given its lower processing temperature and lower extent of damage caused to the substrate by avoiding the high temperatures of sintering. In spite of its advantages, the process suffers from skin effect due to the top-down treatment process which can hinder sufficient curing throughout the entirety of the printed patterns imposing either long-last processing times or the use of high-power plasma with potential for damage to the substrate.
Gold nanorods (AuNRs) are compelling as printable metals compared with other counterparts not only because of their chemically inert nature, but also because their anisotropic structure suppresses the coffee-ring effect and lowers the electrical percolation threshold, giving the potential to generate a conductive trace with low deposition amounts and the ability to be sintered with low power and short exposures to plasma.
We show here the generation of conductive traces by inkjet printing AuNRs when combined with low temperature and low power oxygen plasma sintering. Traces composed of 10-layer AuNRs with resistivity 5e-7 Ωm were generated after 300-second plasma sintering. Compared with spherical gold nanoparticles at equal volume size and weight concentration, AuNRs traces show higher conductivity under the same sintering condition.
Topographical, electrical and elemental analyses are performed to assess the quality of the conductive traces and to confirm the chemical composition of the printed traces and assess the residual presence of surfactant or any residual contamination.
This approach offers a convenient way to print conductive, inert traces that can be interfaced with a variety of flexible surfaces ordinarily not accessible to these methods because of processing limitations.